1. Field of the Invention
The present invention relates to the field of fluid pumps.
2. Prior Art
The present invention is an electrically actuated fluid pump, and in one form, is adapted for use in the automotive market to provide fuel at sufficient pressure and flow rate for use in fuel injected internal combustion engines for vehicles. Accordingly, the prior art relative to this application will be discussed.
At the present time, conventional fuel systems for fuel injected internal combustion engines for vehicles are usually of one of two configurations, namely, fuel systems of the return type or fuel systems of the returnless type. Return type fuel systems are configured in a circulation loop, whereby fuel is pumped from the fuel supply tank through a fuel filter and a fuel rail to a mechanical regulator. Typically, the fuel transfer pump on such systems continuously pumps fuel at a flow rate higher than is needed for combustion in the engine, with the fuel that is not needed passing through a mechanical regulator and being returned to the tank, thereby completing the circulation loop. The fuel transfer pump typically is located in the fuel tank and is an electric pump, such as a gerotor or turbine pump running at maximum speed and electrical current at all times while the engine is running. Because of this, these fuel systems are not very energy efficient, as they typically are not only pumping fuel to the desired pressure for the rail supplying the fuel injectors at a flow rate greater than the engine ever needs for combustion, but at a rate many times what the engine needs at idle and under low load conditions.
Returnless fuel systems use a mechanical pressure regulator located in the fuel tank itself, which is normally supplied by a turbine pump, again running at full output at all times while the engine is running. Thus, bath the return type and returnless type fuel systems have relatively low energy efficiency. Also, the initial performance characteristics of the fuel may be degraded over time due to excessive working, as typical pump outputs are on the order of about 53 gallons per hour (i.e., about 3,333 milliliters per minute). Typical fuel transfer pumps used, have close manufacturing tolerance components making them subject to possible locking up. They are relatively high-speed pumps powered by DC brush type motors that can tend to become noisier over the life of the pump, and may also produce arcing in the fuel tanks, presenting a fire hazard. The constant pumping may degrade the fuel, or at least change the fuel characteristics from the initial values.
Solenoid actuated fuel transfer pumps are also well known in the prior art. A typical fuel transfer pump of this type is in the form of a reciprocal piston (or diaphragm) pump with an analog type solenoid actuator being used to move and maintain (with continuous electrical current) the piston in one direction against a mechanical return spring biasing the piston in the opposite direction. Typically, electrical actuation of the solenoid moves the piston in a fill direction to cause fuel to backfill the piston chamber. When the solenoid is de-energized, the mechanical return spring then provides the fluid pumping force. Consequently, the outlet fluid pressure of such pumps is determined by the force of the mechanical return spring, not the solenoid, so that the output fluid pressure will be independent of the voltage applied to the solenoid for operation thereof.
A solenoid operated fluid pump of the foregoing type is disclosed in U.S. Pat. No. 5,100,304 issued to Osada et al. on Mar. 31, 1992. In the pump shown therein, electromagnets formed by magnetic poles and magnetic coils attract an armature to compress a spring and backfill the pumping piston, with the spring providing the pumping force when the electromagnet is turned off. If a permanent magnet armature is used, as disclosed in U.S. Pat. No. 4,692,673 issued to Delong on Sep. 8, 1987, or two solenoid coils are used so as to be able to attract the armature m either direction, as disclosed in U.S. Pat. No. 3,282,219 issued to Blackwell et al. on Nov. 1, 1966, the spring may be eliminated in favor of solenoid actuation for both directions of motion of the armature. However, pumps of this type typically provide a relatively low output fluid pressure, perhaps suitable for only relatively low pressure delivery of fuel from a fuel tank to an ordinary carburetor on a vehicular engine, or perhaps from a fuel supply tank to a high pressure fluid pump on a diesel powered system, but do not have the capability of providing fuel at the required system pressure for fuel injected vehicles. By way of example, in the '304 patent mentioned above, electromagnets on associated radially oriented poles cause the armature to be attracted axially into alignment with the electromagnets. However, the magnetic field provides only a relatively weak axial force on the armature. Consequently, magnetic circuits of this type may be used to provide a substantial pumping stroke, but not with any substantial fluid pumping force or pressure.
In U.S. Pat. No. 3,282,219 (Blackwell et al.), two solenoid coils are placed substantially end to end so that each one, when excited, will cause an armature doing the pumping to move axially to attempt to center itself longitudinally with respect to that solenoid coil. When the solenoid coil is powered with one end of the armature only partially within the solenoid coil, the solenoid coil provides a magnetic field resulting in a force on the armature substantially perpendicular to that end of the armature, with the field lines wrapping around the solenoid coil and primarily re-entering the armature radially in the part of the armature still protruding out of one end of the solenoid coil. Thus, the longitudinal force on the armature under this condition is proportional to the square of the flux density across the area of the end of the armature within the coil, times the cross sectional area of the armature. However, note that there is a very large nonmagnetic gap in the magnetic circuit, so that the flux densities achievable may be too low to obtain any substantial fluid pumping pressure. U.S. Pat. No. 4,692,673 (DeLong), utilizing a permanent magnetic armature in a multiple coil system, is similar in that regard. In essence, pumps of the '219 (Blackwell et al.) and '673 (DeLong) patents potentially have an even greater stroke than that of the '304 patent, but achieve the large stroke only with a relatively low fluid pumping pressure.
U.S. Pat. No. 5,106,268 issued to Kawamusa et al. on Apr. 21, 1992 discloses an outlet pressure control system for electromagnetic reciprocating pumps that includes the capability of controlling both the frequency of reciprocation and the length of the stroke, The piston of the pump has an armature at each end thereof, each with an associated electromagnetic drive means. The piston and armature are biased toward a center position by springs at each end of the assembly. Half wave rectified electrical power is applied to one of the electromagnetic drive means, with the alternate half wave electrical power being applied to the other electromagnetic drive means, so that one of the electromagnetic drive means is electrically powered at all times. The frequency of the half wave rectified power determines the frequency of reciprocation of the pump, with the voltage of the half wave rectified power determining the pump stroke. The control of one or both parameters is responsive to a pressure sensor in the pressure tank being pressurized by the pump. Because one of the actuator coils is electrically powered at all times, independent of pressure and flow rate, the pump may not be very energy efficient Also, the type of actuator disclosed is of the relatively long stroke, low force type, the long stroke better accommodating control of the stroke, though the low force of the actuators very much limiting the fluid pressure output attainable.